Why do mosquitoes choose humans?

 Carolyn "Lindy" McBride is studying a question that haunts every summer gathering: How and why are mosquitoes attracted to humans?

Few animals specialize as thoroughly as the mosquitoes that carry diseases like Zika, malaria and dengue fever.

In fact, of the more than 3,000 mosquito species in the world, most are opportunistic, said McBride, an assistant professor of ecology and evolutionary biology and the Princeton Neuroscience Institute. They may be mammal biters, or bird biters, with a mild preference for various species within those categories, but most mosquitoes are neither totally indiscriminate nor species-specific. But McBride is most interested in the mosquitoes that scientists call "disease vectors" -- carriers of diseases that plague humans -- some of which have evolved to bite humans almost exclusively.

She studies several mosquitoes that carry diseases, including Aedes aegypti, which is the primary vector for dengue fever, Zika and yellow fever, and Culex pipiens, which carries West Nile virus. A. aegypti specializes in humans, while C. pipiens is less specialized, allowing it to transmit West Nile from birds to humans.

"It's the specialists that tend to be the best disease vectors, for obvious reasons: They bite a lot of humans," said McBride. She's trying to understand how the brain and genome of these mosquitoes have evolved to make them specialize in humans -- including how they can distinguish us from other mammals so effectively.

To help her understand what draws human-specialized mosquitoes to us, McBride compares the behavior, genetics and brains of the Zika mosquito to an African strain of the same species that does not specialize in humans.

In one line of research, she investigates how animal brains interpret complex aromas. That's a more complicated proposition than it first appears, since human odor is composed of more than 100 different compounds -- and those same compounds, in slightly different ratios, are present in most mammals.

"Not any one of those chemicals is attractive to mosquitoes by itself, so mosquitoes must recognize the ratio, the exact blend of components that defines human odor," said McBride. "So how does their brain figure it out?"

She is also studying what combination of compounds attracts mosquitoes. That could lead to baits that attract mosquitoes to lethal traps, or repellants that interrupt the signal.

source:science daily